Hitherto, characteristics of substances have been analyzed by a method of holding a specimen to be measured on an aperture array structure, applying an electromagnetic wave to the aperture array structure on which the specimen is held, and analyzing a transmittance spectrum of the electromagnetic wave, thereby measuring the characteristics of the specimen. More specifically, there is, for example, a method of applying a terahertz wave to, e.g., a metal mesh filter to which a specimen, such as a protein, is attached, and analyzing a transmittance spectrum of the terahertz wave.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2007-010366) discloses a method of holding a specimen to be measured on an aperture array structure (e.g., a metal mesh) having apertures and on a base in close contact with the aperture array structure, applying an electromagnetic wave to the aperture array structure on which the specimen is held, and detecting the electromagnetic wave having transmitted through the aperture array structure, thereby measuring characteristics of the specimen based on a change of frequency characteristics, the change being caused due to the presence of the specimen.
The measuring method disclosed as the related art in, e.g., Patent Document 1 employs, as an index, a change of frequency characteristics caused by the interaction between an electromagnetic field and the specimen near the surface of the aperture array structure. The amount of the change depends on the electromagnetic field that is intensified near the surface of the aperture array structure, the amount of the specimen present in a region of the electromagnetic field, and the value of the complex refractive index. Accordingly, when the amount of the specimen is small, the change of the frequency characteristics is slight and the characteristics of the specimen are difficult to detect.
When the specimen is a liquid, there is known a method using a device called a contact angle meter to measure, e.g., wetness of the liquid. The known method includes the steps of dripping a liquid as a measurement target onto a stationary surface, measuring, with a camera, a size of a round droplet formed by surface tension of the liquid, and calculating a contact angle at an interface between the liquid and the stationary surface. However, it is difficult to measure other characteristics of the liquid as the measurement target at the same time. Another problem resides in that additional equipment, e.g., the camera, is required and the cost is increased.